The principal objectives are as follows: 1. Chemistry of tooth surfaces: Develop clinical procedures for topical fluoridation based on pretreatment with a solution saturated with respect to CaHPO4.2H2O followed by treatment with a basic-phosphate-fluoride solution; test fluoridation solutions containing calcium ions, monomers, or cationic surfactants; develop improved etching and fluoridation procedures for pit-and-fissure sealants and a mechanical test for adhesion of sealant; determine effectiveness of several new remineralization procedures. 2. Solubility of tooth and bone mineral: Measure "solubility spectrum" of enamel as function of position in tooth, location of tooth in mouth, and other natural variables including age, fluoride, and caries susceptibility; continue to develop procedure for study of bone mineral solubility; measure solubility of doped hydroxyapatite and of octacalcium phosphate. 3. Caries mechanism: Establish relative importance of various physicochemical factors in the caries mechanism; seek measures for prevention of caries by altering permselective character of "enamel-plaque membrane".